Genetic improvement of various crop species by genetic engineering has sometimes been hindered because techniques for in vitro culture, transformation, and regeneration of model cultivars are less effective with recalcitrant commercial cultivars.
Barley (Hordeum vulgare L.) is one of the world's most important cereal crops, closely following wheat, rice and maize in total production. Barley is used worldwide for feed, food, and malting purposes.
The ability to genetically engineer barley to improve its performance and pest-resistance or to enhance alternative uses is of great importance. The practical utility of stable transformation technologies is largely dependent on the availability of efficient methods for generating large numbers of fertile green plants from tissue culture materials. Procedures have been described for generating highly embryogenic barley callus and regenerating green plants (Dale and Dambrogio, 1979; Handel et al., 1985; Thomas and Scott, 1985; Goldenstein and Kronstadt, 1986; Lürz and Lörz, 1987; Wan and Lemaux, 1994; Hagio et al., 1995; Dahleen, 1996). However, presently available procedures for producing embryogenic callus and regenerating green plants have been of limited utility when used in transformation procedures for commercially important barley genotypes. These procedures have been hampered by a gradual loss of the embryogenic capacity and regenerability of callus tissue and an increase in albino (chlorophyll-deficient) plants during the prolonged periods needed to select transformed tissue. For example, of the independently transformed callus lines generated by one transformation procedure for the barley genotype Golden Promise, only 51% of transformed lines give rise to green plants and some of these lines regenerated only a small number of green plants (Wan and Lemaux, 1994; Lemaux et al., 1996). When the same procedure was applied to the commercial barley genotypes Moravian III and Galena, none of the resulting transformed lines gave rise to green plants.
There is a need, therefore, for efficient methods for transformation and regeneration that can be used with a wide variety of barley genotypes, including commercially important genotypes.